Cal/OSHA issued fines for violations in a highway construction collapse that injured three workers. This is the latest blow to the controversial project on Highway 101 in Mendocino County, where Caltrans is building a bypass around the town of Willits. We've been following this story for three years.

In Jan. 2015, 150 feet of freeway construction came crashing down. Cal/OSHA has been investigating for months and has now issued citations.

Documents obtained by ABC7 News reveal the three seriously injured workers were on top of the structure about 25 feet high when it collapsed. One had a crushed pelvis and two others suffered multiple fractures.

The accident happened while crews were pouring concrete for an elevated section of the freeway. The work was being done by a Caltrans contractor called Flatiron.

Cal/OSHA found the wooden structure built to support the project failed. They said in their citation the structure called "falsework was not properly designed, was not erected as per the design plans, and deficiencies were not identified when inspected by the project engineer."

Flatiron is the same company working on the Doyle Drive replacement project leading up to the Golden Gate Bridge.

Flatiron was working with another contractor called DeSilva Gates on the Willits project. Altogether, the two companies and Caltrans face a total of $165,000 in fines -- most of it to be paid by Flatiron.

Flatiron also sent a statement say it is "committed to keeping our projects as safe as possible, and we will continue to cooperate during this process."

Caltrans said, "Safety remains Caltrans' top priority and we will continue to work with Cal-OSHA and our contractors to ensure the safest workplace possible while we move forward on this critical project."

The collapsed section has now been rebuilt. Flatiron will pay the additional cost. Caltrans estimates the entire six-mile bypass will cost taxpayers $300 million.

DeSilva Gates had no comment and there's no word on whether the companies or Caltrans will appeal.